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Jul 21, 2013, 04:11 PM
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FAQ

RC Cars FAQ (though aimed @ Electric Powered Cars, there's info for other types too!)


tHello fellow car drivers, and those aspiring to drive one. It came to the attention to some of the "regulars" here that quite a few questions keep getting asked over and over, so it seems a FAQ thread for some of those common things might be helpful. This thread attempts to fulfil this role, and with the contributions of some that have years of experience in running battery powered cars, we hope to be able to help others out.

This FAQ thread is a work in progress, if you find you are missing info that should be here, you're very welcome to ask or contribute. This is not a personal effort, the aim is to channel the experience that is present here on these forums, but is not easy to retrieve with a simple forum search.


As a preliminary template, the FAQ will be made up of several chapters, each covering an area in RC cars. This structure might be altered at some point, should that prove to be more convenient. We'll just have to see how it goes.


Table of Contents

- Part 1: Different Vehicle Types, Motors & Batteries, and Transmitters (fist posting in this thread)
- Part 2: Suspension, Drivetrain, Wheels and Tyres, Maintenance and Upgrades (second posting in this thread)
- Part 3: Advice for buying a Used RC Car (third posting in this thread)




Part 1, covering Vehicle Types, Motors and Batteries




Different Types of Vehicles



This is often the first thing an aspiring driver asks himself, and later, others. There are quite a few different types of vehicles, each with their benefits for some, and drawbacks for others. We will list the common types here starting with off-road, and give an example picture with each type, to give a general impression of how it looks:


Offroad options


Buggy: Classic type, designed to go fast over terrain, often relatively lightweight, and with low center of gravity, which means the ride height aka ground clearance often isn't very big. Depending on scale/size this may limit the ability to handle rough terrain but this need not be a problem. Also very allround, if you fit road tyres, and lower the ground clearance, it can be very fast onroad as well.

Here are a few examples of classic buggies, the Kyosho Optima Mid, and the Team Associated RC10:





Older buggy designs tended to have the weight more to the back, some newer designs tend to focus on having more downforce on the front wheels as well, to help with steering, often resulting in the "cockpit" of the body shell being more forward swept.




Truggy/Stadium Truck: These 2WD cars feature wide, bigger wheels than buggies, and are often fitted with longer suspension arms, making the car wider as well, to maintain stability, in spite of the higher center of gravity that comes with the better ground clearance. Bodies often resemble some kind of pickup truck, but can also lean a bit more towards phantasy designs. Still suitable for racing, can be quite fast, and the bigger ground clearance gives the option to handle rougher terrain than a buggy might be able to.




Truggy: Bit like a Stadium Truck, but 4WD.


Monster Truck: Big wheels, often with a V-shaped pattern, and the bofy mounted very high above the chassis. As their real life counterparts, built to run over big obstacles and look good doing it. Less suitable for racing, but still fun to drive.



Short Course Truck or SCT:
Also bigger wheels, like a Truggy, but more narrow, and looking more like a pickup truck. Usually a little bigger and heavier than other cars in the same scale (in the 1/10 scale class these SCTs are sometimes referred to as being more 1/9 scale) giving the car more inertia. This often results in the car handling more like a real car, like more diving of the nose when braking, or leaning in a corner. This realism, combined with the excellent terrain handling capabilities, and the fact that it's very well possible to race this type of car, has made it gain popularity over the last years.




Scalers/Crawlers:

Designed to overcome large obstacles. Big wheels, with lots of traction, combined with slow running, high torque motors, combined with a chassis that allows a lot of free movement for the axles, help this type of vehicle to achieve that. If you like a different challenge, and want to drive where most vehicles can't come, this might be the type of car for you.






Onroad options



Pan cars:

Relatively simply design, meant to go fast on a flat surface. Rear wheel drive, chassis is usually a plate, and the suspension is using rubber rings, or sometimes a very short shock. Some designs use chassic flex as "suspension" or another flexing part. But despite this apparent simplicity, setting it up to get good grip at the high speeds these cars can reach, is not that simple.





Touring Car or TC:

Also mostly meant for onroad, but more complex than the pan car. 4WD drive, and full indenpendent suspension. The 4WD makes these easier to drive for beginners, but the added complexity means, just like with 4WD vs 2WD buggies, that the top speed with the same motor and battery will be lower. Some even have the option to increase ground clearance, and turn the TC into a little more offroad capable vehicle, a rally car. Or fit low grip tyres, and some modifications, to turn it into a driftcar.



A bit in between on- and offroad are Rally-type vehicles. Often fitted with a scale like body, resembling a real rally car, just like the Touring Cars, but with better grond clearance, and more thread on the tyres.


Formula 1:

Like the title says, scaled down F1 racers, 2WD.




1: What kind of car should I choose?


With the above information in mind, the first question should be, where do you intend to drive it? If you want to run offroad, obviously an onroad car won't be the best option, but even with offroad, there are various grades of how rough the terrain is, and what car will handle it best. Same with onroad, a carpet racer won't run well on a parking lot if it's now smooth enough.



2: What is better, 2WD or 4WD?


It's actually not a matter what is better, as each vehicle type has it's merits and drawbacks. 2WD means a more simple drive train, so most likely less maintenance. The less complicated drive train also means less drag, so with the same motor, battery, etc, a 2WD vehicle will most likely have better acceleration, better top speed, and longer running time. Also, since there are no driven front wheels that spray dirt etc all around over the body and rear suspension parts, you will typically have less cleaning to do after running of a dusty terrain. Plus it's fun to make a rear drive car make donuts, and slide through corners.

Drawback of 2WD is that it's easier to get stuck on terrain, if one wheel is lifted from the ground, and the drive train has a free moving differential, the wheel that is still on the ground will not have traction. With a 4WD you will stil have 3 wheels that can keep the vehicle moving.

Besides this trait of 4WD, better traction, cornering is usually also easier, as the front wheels help "pull" the car around the bend. Since you can also brake on 4 wheels (as braking with an electric driven car is done by locking the motor) you have better brake power, even though a 4WD vehicle will usually be heavier than it's 2WD counterpart. All this makes a 4WD vehicle easier to drive for beginners, whereas a 2WD rear drive vehicle can "hook" in a corner, or do a 180 turn if you are too eager on the throttle, on a surface with less grip.

Still, the easier construction of 2WD vehicles, and their usually lower price tag, still makes these also an excellent choice for new drivers. Personally, I prefer to have both types around.

P.S. don't be fooled into thinking that a 4WD with front drive train disconnected will be a way to experience 2WD driving so you can have both with a single car, as a 4WD vehicle without 4WD will usually just feel like what it is, a crippled 4WD vehicle, and lack the fun driving traits of a true 2WD one.


3: What is the best scale to buy a car in?


A new driver will soon learn that RC cars come in different scales and sizes. Very small, like the 1/36 scale Losi Micro T, to very large 1/5 scale buggies. Just like with 2WD vs 4WD it's not really a matter of what is best, but where do you want to drive your car. A smaller car will be more affected by obstacles on the track, where a bigger car will not even be fazed by that same obstacle. A smaller vehicle will be easier to carry around, and require less storage space. But with a bigger car you are less limited to where you can drive, no need for an ultra smooth running area.

If you want to stay a little allround, 1/10 is a good starting point. While lacking the "nothing can stop this car" abililty of 1/8 scale and bigger, it's still quite capable running offroad, and less "nervous" than smaller 1/16 or 1/18 scale cars. A 1/14 scale buggy with relatively large wheels, like the Losi Mini 8ight, and more recently, the LC Racing EMB Buggy (also known as the Tacon "Soar") combine quite good offroad performance, with a smaller size car.


4: Is it still possible to get a kit, it seems like everything is RTR these days?

Especially for those that recently returned to this hobby, after building their first kit many years ago, it may appear no kits are sold these days. But this is just a matter of how things are advertized, most people nowadays want to be able to drive right away, so that is what you see offered. In fact there are still many kits available. Vehicles designed for competition are almost exclusively sold in kit form, brands like Durango, Kyosho, Schumacher and Xray, to name a few. But also cars aimed at more casual drivers can be found as a kit, Tamiya still has a large selection of kits. Other options are Team C, and I may be forgetting some.

Browsing this thread Paul created might also help: https://www.rcgroups.com/forums/show....php?t=2161773


5: I got myself a kit/new body, how do I paint it?

Since most bodies are made from clear plastic, called lexan or polycarbonate, some things need to be observed. This material remains flexible, so the paint applied should be able to flex with the body. Hard enamel paints will chip off easily. You will need special paints that are designed for this material. Some people have gotten good results with vinyl paints, and there are other options, but if you want to stay safe, get the proper paint.

A clear body is painted on the inside, instead of the outside. This way, there is far less risk on paint damage should the car hit something. Before applying the paint, the body should be washed with a mild cleaner, like a dish washing agent. Make sure it's rinsed well, or the paint won't stick.

Optionally, you could scuff the inside of the body with something like a scotch brite sponges (be careful not to rub over the windows!) as this could give even better bonding between paint and body. Don't overdo it, just enough to dull the inside surface a little. Don't worry about the paint job going to look bad, once paint is applied to the inside, and the result will look crystal clear again.

Good chance you want to mask certain parts of the body, like the windows. This can be done with tape, preferably special masking tape, as regular tapes are often harder to form around curves and may leave some glue behind after removal. Another option is Liquid Mask, which also makes it possible to mask intricate designs. One warning, make sure that the paint you use is compatible with the masking fluid, or your design can be ruined within minutes.

It's also wise to do the trimming of the body to fit the car before paint is applied. It's very easy to damage the fresh paint, if you cut the body to shape afterwards. Also, it's easier to mark the mounting holes, when the body is still see-through. Best just to mark these holes, but not drill them yet, as paint can run through the holes to the outside, while painting.

If your car has a wing, like a buggy, there are 2 options for painting. Applying paint to the underside will look better, as the wing will have the same high gloss finish as the body. But if the car gets hit from behind, or makes a wheelie, the underside of the wing can get scratched, and paint can wear off. If the upper side of the wing is painted instead, such an accident will only leave some scratches, but the paint is safe on the other side of the wing. It's matter of added durability vs better looks.


For more tips and tricks regarding painting, check this thread: https://www.rcgroups.com/forums/show...9#post27592601



6: What do all these car-specific words mean?

Though some parts that make up an RC car are discussed in detail later on, here's a small glossary covering some common expressions. Check the pictures to aid in identification of the parts.


1) A-arm: lower suspension arm, one side is attached to a pivot point on the chassis, the other to the block holding the axle

2) Steering Knuckle: part that holds the front wheel axles, and allows the wheels to turn left and right

3) C-Hub or Castor Block: as the first name suggests, the C-shaped part that holds the steering knuckles. Usually only found on the front, unless the car has 4-wheel-steering (4WS)

4) Rear Hub: Holds the rear axle

5) Bulkhead: Part of the car that is attached to the chassis, and to which the suspension arms, shock mounts and upper arms are connected to. Can also be the housing for the differential.

6) Shock Tower: Usually attached to the front and rear bulkhead, a frame that the top end of the shocks are attached to





Servo Saver: A mechanism that softens the impact to the servo when the wheels that can steer, hit something, and are deflected to left or right. This reduces the strain on the servo gears and motor. The picture shows a type that is installed on the servo, but it can also be present somewhere else in the steering system, like in the levers between wheels and steering link that is attached to the servo.




Motors, Batteries and Transmitters



1: What's the difference between brushed and brushless motors?


Simple answer would be, one has brushes, one hasn't. But that's a little too simple perhaps. In a brushed motor, the brushes deliver current to the commutator, a series of metal strips, that each are connected to a coil in the motor. When a battery is connected to the 2 motor terminals, current starts flowing through those brushes, to the coils, making these magnetic, causing the axle to spin. Reverse the polarity of the terminals, by switching the wires, and the motor starts turning the other way. This type of motor has simple wiring (2 wires, that's all) and is quite cheap usually. Performance can be pretty good too, there is just one catch. The friction between commutator and brushes causes these to wear down, and eventually the brushes need to replaced, or the motor needs a new rotor, as a worn commutator can't be replaced. It's possible to clean the surface of the metal patches of the commutator some times, for instance by using a special lathe tool, but as this removes material from the surface, at some point it's over. Also, the efficiency of this type of motor isn't very high, as the friction turns energy to heat.

Brushless motors don't have this problem, as there are no brushes and commutator to switch on and off the current to the motor's coils. Instead the motor is connected to the speed controller with 3 wires, and the switching of the respective coils is done electronically, in the speed controller. This makes a brushless speed controller more complicated, and also more expensive. But in return you get almost zero wear on the motor, just the bearings that may need replacement sooner or later, depending on track conditions, and the motor can run more efficient, converting more of the battery's power into motion, instead of heat.


2: Do I need to break-in a new motor?


This depends on the type of motor. A brushless motor has no commutator that the brushes need to wear in to, so no break-in is required. With a brushed motor, proper break-in will yield a faster running motor, with longer life expectancy. There are a couple of ways to do this:

- Most simple method, take it easy the first runs. Don't run full throttle, and get the car up to speed gradually. Drawbacks, the motor does get to work, so some arcing and commutator surface damage may occor. Also, it takes a lot of self control to go easy on a new car for several batteries.

- Also pretty simple to perform, but easier on the motor. Put the car on a secure stand, so the wheels are not touching the ground, and use the throttle trim on the transmitter to let the motor run at low rpm. Added advantage is that the gears get the chance to run in a little without any load. As a variation on this, it can also be done without the pinion on the motor axle, for lowest possible motor load, which in theory should be a little better for the motor.

- Wet method. This involves putting the motor in (preferably demi) water, and connect the motor wires to a 2.4 volt power source, like 2 AA batteries. As the commutator and brushes are not exposed so air, there is no arcing possible, to less chance on commutator surface damage. The water also acts as polishing agent, and provides some cooling too. After a while the water will become greyish or black, showing the worn down brush material. Disconnect the battery, and remove the motor from the water. Dry it out well, flushing the motor with electric motor cleaner tends to work well, or a blow dryer, or putting the motor in a bag of rice. When properly dried, remember to oil the bearings. This method is claimed to yield the best results, but it's a bit more messy, and if the motor is not dried well enough, rust can occur.

P.S. for some advice to keep your brushed motor in good shape, check the next posting, for the header "Caring for brushed motors"


3: How much heat can RC components take?


Though one motor can take higher temps than another, depending on things like magnets used, insulation of the winds, etc, it's better to be rather safe than sorry. Safe temps are:

Battery < 120 (around 50 degrees Centigrade)
ESC < 140 (around 60 degrees Centigrade)
Motor < 160 (around 70 degrees Centigrade)

A little higher doesn't have to result in instant damage, but it's best to stay below these values



4: How do I treat LiPo batterues, and can I use lipo batteries with a brushed motor?


Starting with the second part of the question, as often the advice is to convert a car to brushless and get a lipo battery, when upgrading, it might seem that those 2 should go together. But it's perfectly possible to take this upgrade path in steps, like first getting a lipo battery, and perhaps later, if more performance is needed, put in a brushless motor. A brushed motor can run of a lipo battery just as happily as it can run on NiMh or so. The only thing to watch is that the motor typically will run about 10 to 15% faster, and this can cause more heat to be generated. Also, as LiPo batteries often have higher capacity in mAh than NiMh or NiCad, you will most likely run the car longer before having to change the battery, which can cause the motor to get even hotter. So if taking this step by step upgrade path, make sure you check motor and ESC temps at least the first few runs, see if nothing gets much hotter than before. An Infrared thermometer is the best tool to compare temps, with fingers it's much harder.

P.S. most vehicles that come with a brushed speed controller, especially RTR ones, don't have a protection circuit built in to warn/prevent deep discharge of a LiPo. So you may need to get a seperate LiPo saver/monitor gadget, that keeps an eye on the battery's voltage while driving.

!! Important !! LiPo batteries require special care, and become unstable, damaged, even dangerous (possible fire hazard) when overcharged, drained too far, or getting punctured. If you got your car RTR, with NiMh battery pack, you will also need a different charger. There are lots of options, but a good basic start would be a B6 charger, or similar "4-button-charger".

Also, since the battery can't take getting drained too low, you need some kind of protection. Check your ESC's manual if the LVC (Low Voltage Cutoff) can be set to LiPo mode. If this isn't possible, a separate lipo-alarm/monitor/buzzer would work as well. An experienced driver may notice when the LiPo is getting close to being drained, and stop running before that happens, but a backup monitoring system, like a buzzer, might still be smart to have installed.



5: My motor is running the wrong way! What is going on?


First, never swap the ESC battery wires! This will not make the motor run the other direction, instead it will smoke your ESC!

Having said that, there are a few things to check. If the car is not a crawler, so the ESC has brakes or you can set the ESC to use brakes, check what happens with the motor when you go from giving forward throttle on the transmitter, to reverse. If the brakes come in, you can be sure the ESC is seeing the throttle trigger as going forward. If the wheels slam right into reverse rotation, check what happens when you go from reverse throttle trigger position, to forward. If the brakes do get active then, the throttle direction is reversed. This can be solved by operating the "servo-reverse" switch for the throttle, or on a computer-based transmitter, activate that in the transmitter's menu.

If the ESC responds well to forward, and invokes brakes when going into reverse coming from forward, but the motor still runs the wrong way, more action is needed. We can have 3 situations:

- Brushed Motor. Simply reverse the wires between motor and ESC. NEVER switch the battery wires, thinking hooking up the battery with polarity switched will make the ESC work reversed. It will just damage or kill the ESC...

- Brushless Sensorless Motor: Swap any pair out of the 3 motor wires between ESC and motor, and the motor will run the other way

- Brushless Sensored Motor: No wire swapping here! A sensored motor can only be connected to the ESC in one way. To reverse direction, often a programming card is needed. If that is not an option, and it's a 4WD shaft driven car, you could use this trick, take out the diffs, and put back 180 degrees turned, if possible. Since the crown gear will be on the opposite side then, the wheels will run the other direction, even though the motor still runs the wrong direction. Make sure you change both front and rear diff, turning over only one diff on a 4WD car will lock your entire transmission!



6: What's with poles and winds/turns? My head is spinning...

Let's start with a brief explanation of how a motor is made up. An electric motor uses magnets and coils to transform electric energy from the battery into motion. In a brushed motor, inside the cylindrical can are 2 permanent magnets, and the armature, the part that spins, has ferrite anchor shaped parts, on which wire strands are wound. Here's an example:



It's possible to have more than 3 poles, as long as the number is odd, and not even. As for RC cars high rpm is needed, the common configuration is 3 poles and 2 magnets. But not all 3 pole motors with 2 magnets will perform the same way. Here is where the number of turns or winds, referring to how many times a strand of wire is wound around the T-shaped segments. The more turns/winds, the lower the motor's rpm will be, but the higher it's torque. The lower the amount of turns, the faster it will run, and overall have more power as well, but it will draw more current, and require to change to a lower pinion (see a few questions below this, about "lower gearing") to avoid overloading the motor.

It's also possible not to wind a single strand of wire, but 2 wires, or three. This is called "double wind" or "triple wind", and it also affects the motor's power "character". A "single" will usually have more punch in the lower RPM range, while a double or triple will have it's punch on a higher rpm. This allows motor manufacturers to create motors with different behavior, despite having the same number of turns/winds.

A brushless motor is a somewhat a mirror image of a brushed motor. Instead of the armature with the coils rotating, the coils are now fixed in the motor can, and the armature consists of permanent magnets, which rotate instead. The number of coils is still usually 3, and the number of magnets 2 again, alhough motors with 4 magnets are also commonly used in RC. 4-pole motors, as these are called, will have noticably more torque, so a bigger pinion can be used, and/or it can be used in heavier cars, where the extra torque is needed to get the vehicle's acceleration up to an acceptable level. Addional benefit is that because it has higher torque, it's less likely to get overloaded (as long as you don't fit a 1/16 scale motor to a much bigger can for instance) and will most likely run cooler than a 2 pole motor that has the same power output. Make sure though the gears in the transmission can handle the extra torque.


7: If I fit a bigger battery, will I fry my motor and/or ESC? And what is with the C-rating?

First, lets address a common misconception about motors and batteries. A battery doesn't "push" current" to the motor, the motor "pulls" (or more often used term, "draws") current, enabling it to run. So, if you simply take another battery with the same cell count, but higher mAh (content, or "electric fuel capacity") you won't get a faster car, but you will be able to run longer. If you are using the same type of battery, your car might even go slower, as the increased weight reduces acceleration and top speed a little. Beware, when using a bigger battery, and run the car longer without breaks, the motor and ESC may get much hotter than before. Check your temps regularly!

Things will get more interesting when C-ratings come into play. The C-rating describes the relation between capacity of the battery in mAh and the max current it can sustain continuously. If you have a 20C 3000 mAh battery, it can theoretically sustain a current of 60000 mA or 60A. If you fit a 30C 3000 mAh battery, able to deliver up to 90A continuously, your car won't be faster, as we learned that the battery doesn't push this current.

However, especially when RTR cars are involved that are sold with battery, it's common that the stock battery struggles to deliver the current the motor demands. This will cause the battery voltage under load of the motor to drop, and the lower the voltage, the slower the motor will run, so the slower the car will be. If you replace this struggling battery with one with higher capacity but same C-rating, or same capacity but higher C rating, or both, higher capacity and higher C-rating, the motor will more likely get the current it needs, voltage under load will be higher, and your car will run faster than before. When making such an upgrade, and you notice your car running much faster than before, watch the motor and ESC temps, as it will get hotter than with the stock battery, that more or less acted as a performance limiter.



8: What rating should my ESC be when I know the specifications of my motor?


Before answering this, let's first address a common misconception about the current that runs between battery, ESC and motor. A battery doesn't push current but it supplies current. The motor draws current as it has to work to get or keep the car moving, and the ESC can be seen as a "valve" allowing current to flow between battery and motor, and regulate that flow. If the battery is not powerful enough to supply the demanded current, it will have it's voltage dropping or even collapsing, and might also get hot. The motor won't be able to perform to it's fullest possibilities. If the ESC can't really handle the current that flows through it, it will either go into thermal shutdown, a built in safety to avoid permanent damage to the ESC, or, if this safety system is not present, or things happen to fast for it to respond, the ESC will go up in smoke. So it's better to choose the ESC a little on the safe side, so it should be able to handle more current than the motor can possible demand from it.

Some think you also need to choose the ESC not too powerful, so one that can handle 200A connected to a 100A max current motor will make the motor go up in smoke. But as we have seen before, current doesn't get pushed, so that 200A ESC is not going to cause 200A to run through that 100A motor (unless it has a short circuit) and motor and ESC are perfectly safe to use in this combination. The only reason not to go overboard when getting an ESC that is rated higher than the motor, is that it will most likely be more expensive, and it's not needed to spend the extra money on a more powerful ESC.


9: Can I keep using my current NiMh batteries with my new brushless motor?


This question naturally spins off from the previous one, as this is also a possible step by step upgrade path. Though possible to use NiMh with a brushless setup, depending on how powerful the motor is, the batteries might struggle to keep up, and can overheat. Same as with the LiPo/Brushed motor combination, check the temperature, in this case of the batteries. If getting too hot to touch (again an IR temp meter would come in handy) this indicates the batteries are struggling, and this can cause capacity loss (a too hot NiMh will vent some of the gas inside through a safety valve) or could even be dangerous. If you have really good quality, true racing spec, NiMh batteries, it could work out fine, but a LiPo will be faster, and can cope better with the higher current draw of the upgrade motor.


10: My car came with a speed controller that uses a servo. Can I replace it with an electronic speed controller?


Before electronic speed controllers (or ESC for short) became common, many car kits were fitted with a mechanical speed controller. These servo operated devices usually have 3 step control, using a switchboard to set one or more high power resistors in series with the battery's voltage. It's crude, but it works. Main drawback is no smooth startup, putting a high initial load on motor and drive train, no gradual speed control, and when driving slower than full speed, part of the battery's energy was converted to heat, as it was "burned" in the resistor. Replacing a mechanical speed control is easy, practically drop in, and is a must-do upgrade, unless you want to keep you older car fully stock, including the crippled speed control method. But if you do upgrade, you will be able to experience you car like never before, and due to the smoother startup, it will also last longer.


11: Someone told me to gear down on my car. Do I need a smaller pinion and/or smaller spur?


There is some common misconception about what gear to change when wanting to gear up or gear down. Basically, when someone talks about a "lower gearing" it means a bigger reduction of RPM between motor and the wheels. Just like in a car with manual shift, in 1st gear you have the biggest reduction, so you get better torque, to help get moving from standstill, but no good for top speed. When you shift up, the gear ratio changes, and motor rpm is less reduced, resulting in less torque, but better top speed.

To get this effect in an RC car, you can select different pinions or change the spur gear, or both. If you want to gear down, so get a bigger reduction of motor RPM, you can:

- Take a lower teeth count pinion
- Take a higher teeth count spur gear
- Both

If you want to gear up, for instance to get higher top speed, you can:

- Take a higher teeth count pinion
- Take a lower count spur gear
- Both

For some more excellent information about gearing, like what to do when upgrading to a different motor for instance, check this thread on Bill Delong's Blog: https://www.rcgroups.com/forums/show....php?t=2298334



12: Talking about gearing, what is "gear mesh" and how do I set it right?


Gears need to be at a certain distance from each other to run at their best performance. Too close and the gear's teeth will wear down, as well as cause binding in the drive train. Too loose and you run extra risk stripping the teeth clean of the gear. The way the gears "bite" into each other is called the gear mesh.

To set this properly, there are a few methods. One that is very commonly used is putting a sheet of regular (80 grams or close) paper between the teeth of the gears, the slide the gears towards each other until you can't move these any more. Tighten the motor screws and check if the transmission runs smoothly. This can be hard as the motor will have a certain resistance due to the magnets inside. To temporarily eliminate this, you could loosen the set screw holding the pinion on the motor shaft, such that the pinion can turn freely on the motor shaft. If you move the car forward and backward manually, you can feel just the drive train resistance, including the gear mesh you just set. If adjusted properly, you should feel little difference between the resistance with the pinion on the motor shaft, but still loose, and no pinion on the motor shaft.



Some also check the gear mesh, or fine tune it after using the "paper method" by listening to the noise of the gears when running the motor. Usually less noise means less resistance, and better gear mesh.


13: No matter how I set the gear mesh with my new pinion, the gearing stays noisy and my pinion and spur wear down very fast. Help!

Apart from setting the gear mesh properly, there are a few pitfalls that can shorten the gear life and limit performance. First, the material the gear is from. Some brands still use brass pinion gears for cars in 1/10 scale. Perhaps with some low power, stock motor, that makes the car go 25 km/h, that will do. But as more powerful motors are used, the brass pinion will wear soon, and proves to be less durable than plastic.

Second pitfall is the gears pitch, also called "module". This is a number that describes the ratio between the gear's diameter and teeth count, and thus defines the spacing of the teeth, and their shape. Never mix gears of different module/pitch! Even when some types may look compatible, that is only true if the gear's pitch is an exact match. Ignoring this means shorter gear life, more noise, and lower performance. So when getting a new pinion, don't just look at the teeth count, but also verify the pitch. If you can't find in the documentation that came with the car what pitch is used on the gears, you can use the calculator on this page to determine the gear's pitch: http://scriptasylum.com/rc_speed/gear_calc.html

Btw, another possible cause for higher noise and pinion/spur wear could be that the rest of the transmission is binding somewhere. So if you haven't already, remove the pinion from the motor axle, and feel if the car is running smoothly, with minimal resistance.



14: My motor is running very hot, what can be wrong?

This can have a number of causes. First, it's best to determine just how hot it is. Just touching it with a finger can give an indication, but even 50 degrees centigrade (122 Fahrenheit) can feel pretty hot, but is still perfectly safe for a motor. Best way to check the motor temp is an infrared temp gun. No need to contact the possible hot surface, and you get a good indication of the true temperature.

Critical temps are in the range of 90 degrees centigrade (200 degrees Fahrenheit) and it's well advised to stay a good bit below this limit, like 70 degrees centigrade (160 degrees Fahrenheit). Overheating a motor can cause the magnets to start loosing their magnetism, and this process is irreversable. Once a motor's magnets have faded due to overheating, the motor will have less torque, and overheat even faster the next time the vehicle is run, causing more damage to the magnets, it's a downward spiral if no action is taken. Apart from the faster heating up of the motor, you will also notice the car running slower, and with less acceleration.

Common causes for a hot running motor are excess drag in the drive train, motor geared too high, or too low, causing it to "freewheel" a lot, no airflow over the motor, and some more things.



15: Do I need fans to cool my motor/ESC?

If something gets too hot, it's always better to see what is causing it, and preventing the heat buildup. Forced cooling, like with fans, is more like a bandaid. Like mentioned above, solving hear issues could mean changing the pinion gear, drilling a few holes in the body to direct airflow over the hot components, etc. However, in some situations that might not be a direct solution. Also, even when you manage to keep the temps within safety margins, running cooler can improve performance (for instance when things heat up, their electrical tesistance often increases) and lengthen the life of the used components, like the motor, ESC, etc.

Some ESCs come without fan as it will not be needed to keep it from overheating, but have the option to attach a fan to the heatsink. It can even be that the ESC already has a socket where to plug in the fan. If not, you could have it connected to the receiver, but beware that the receiver can't deliver too much power. Also, drawing more power from the receiver will mean that the BEC circuit in the ESC will have to work harder, and this can cause the ESC to heat up faster. It could even be that the benefit of running a fan on the ESC is totally negated this way, as the ESC heats up faster due to the extra load on the BEC, than the fan's cooling effort. A solution would be to use a seperate BEC for the fan, or connect it directly to the main battery's voltage, of the fan's specs allow this.

Same precautions should be observe when adding fans to a motor, make sure it doesn't draw power from where it shouldn't.



16: What's "Timing Advance" on a motor and what does it do?


Though this applies to brushless motors as well, it's easier to explain taking a brushed motor as example. Simply put, timing advance refers to at what moment the coils, in this case on the armature, get energized. This has some benefits, as well as drawbacks. With neutral timing, the motor has the best torque, good power, and best efficiency. Let's take some arbitrary numbers to make this more clear. We set the power with zero timing on 100 watt and efficiency on 80%. This means, theoretically, 80% of 100 watt, 0r 80 watt is available for propulsion of the car, and 20 watt goes to friction, heat, etc, so is lost.

Now we increase the timing to 12 degrees, again an arbritrary number, not actual motor data from a specific motor. The motor's rpm will increase, torque may decrease, and total power goes to 125 watt. However, effciency drops to 75%. This means the motor will output 75% of 125 watt = 93.75 watt, so quite a bit more. However, it now loses 31.25 watt on friction, heat, etc, so it will run a little hotter than before.

Suppose you turn it up another 12 degrees and the power goes to 150 watt with 65 % effciency. This means you get 97,50 watt, a small increase, but the power loss in heat etc is going over 50 watt. This means the power increase gets negated by the far reduced efficiency and extra losses in heat. So this means there is a turning point, where the increase in power isn't worth the losses in efficiency of the motor. With a brushed motor, increasing timing very far also has the drawback of increased brush and commutator wear. With brushless motors this doesn't occur, but apart from that, the same applies that above a certain timing setting, there is no real increase in output power, and the motor just burns more of your battery's energy into heat, than it does in extra performance.

Without a motor-dyno (device to benchtest a motor) it's harder to find this turning point, but a good alternate is to check motor temps often when adjusting timing settings. And also keep in mind that a higher timing setting reduces torque, so you may need to use a smaller pinion gear to compensate for that.



17: What's the difference between sensored and sensorless brushless motors?


Short answer, one has sensors, but that still doesn't explain much, naturally. To make a brushless motor run in a certain direction, the ESC needs to activate the coils inside the motor in a specific order and frequency, to make the motor run smoothly. In a sensorless motor, the ESC uses some clever trick, to "guess" the position of the rotating part of the motor (rotor) and adjusts upon that. This system is more prone to error, especially when the car is coming from standstill, there is a change the motor will start to run choppily, as we will see covered in the next question, below this.

With a sensored motor, there are some small sensors inside the motor, and there is an extra set of wires between motor and ESC, for the sensor data. With that the ESC knows the exact position of the rotor, and can better control the motor. As a result, a sensored setup tends to run smoother, as there are no "bad guesses" about the rotor position. It may also feel like it responds faster, due to this.

Mind you, some sensorless setups can also be very smooth, but if you want the ultimate throttle control, sensored is the way to go.



18: My sensorless brushless motor is running very choppily. What is wrong?


First, it's important to determine if the choppy running is only at low rpm, like when coming up to speed from standstill, or at any motor speed. The latter could be a sign of a bad contact somewhere, like in the motor wiring. A cold solder joint, partially broken wire, etc.

If it happens only when coming from standstill, the infamous cogging, there are other things to check for.

- One option is that the motor has too little torque to get it up to speed from 0. If that is the case, fitting a smaller pinion gear, or bigger spur, will help.

- Another solution could be to alter the timing setting on the ESC, if possible.

- Finally, the ESC can play a big role. On a sensorless system, the ESC has to "guess" what direction the motor is running, and what coil to energize next. Some ESCs are better at this than others, so that will affect how smoothly the motor will run from standstill.



19: Breaking in new NiMh batteries/Reviving old NiCad/NiMh batteries

When you get a second hand car, or dig up a car from your youth from the attic, the batteries in that car have not been used for a while. Often people connect these to a charger, to see if these still work, and set the charger at 1A or higher, like around 1C, fast charge, battery fully charged within the hour. Common thing then is that the charger declares a full battery after a few minutes, but when run in the car, it will prove to be almost flat. The reason for this is that the old NiCad/NiMh cells need some "exercise" to get into shape again, assuming the battery didn't just die of old age, or started leaking, and is now damaged beyond being usable. If you were to watch the voltage during such a charge attempt, you would see it rise rapidly, and then drop off just as rapidly, triggering the charger's battery full detection circuitry, so it declares a "battery full" condition, in error.

Same applies to fresh NiMh batteries, these also need a "workout" to get into shape. Best way to revive such a "tired" pack is to charge it slowly the first 2 or 3 times, just like with a new one. So set the charge rate at about 0.1 or 0.2C, in case of a 2000 mAh battery that would be 0.2 or 0.4A. If the battery is still ok, and only out of shape, you will see it will now take a full charge, or close to it, and depending on how high you set the charge rate, take up to 14 hours to declare battery full condition. Perhaps you can drive, and discharge it in your car, but it might still be too weak for that. In that case, use the discharge program of your charger, if it has one, and set to about 0.5A discharge rate. After the battery is depleted, run another slow charge, but you can try to up the charge rate a little, like 0.5C or so. If the battery responds well, it should again take a good full charge, and if you already ran it in your car after the first charge, it will probably perform better now.

Depending on how well the battery responds to this "workout", you might be able to get it up to 1C charge, or even higher, although this only applies to good quality cells, that are still in good condition. Some new NiMh or NiCad batteries can't even take 1C charge rate when new.



20: Can I use the transmitter I have with a new car?

That depends. 25 years ago, before 2.4 GHz equipment entered the RC hobby, just having a transmitter and receiver on matching frequencies and modulation type, AM or FM, was enough to ensure compatibility. That simplified things, although you had to be on the watch that no one was using your frequency at the time you were operating your model. If you ran/flew/controlled a boat with other people together on a regular basis, this implied bringing along several transmitter and receiver crystals, so you could make a swap if that was needed.

2.4 GHz changed this, as along with the higher transmission frequency, control signals were added, as well as "frequency hopping", and receivers and transmitters got their own unique ID. Once a transmitter and receiver were matched, a proces called "binding", these would remember their connection. As a result, if you were operating your model, and someone else came along, and switched on his transmitter, even if this other person would have his transmitter at the same frequency, your receiver and transmitter would stay connected, and just "hop" to a free frequency automatically, to avoid interference or loss of control.

With this ID-system, transmitter brands also introduced their own "transmission language" or protocol. This broke the inter-brand-compatibility of the older FM transmitters, meaning once you had a transmitter of a certain brand, you were forced to use receivers of the the same brand, or a brand name that sold the same equipment, but just with a different brand name, or re-branding.

So if you buy another car, and your first car came with a 2.4 GHz transmitter, you will only be able to control the second car with that same transmitter if:

- the new car is from the same brand or a brand using the same transmitter protocol
- you buy a seperate receiver that is compatible with the transmitter you already own, and fit that to your new car

Horizon Hobby has succesfully picked this up, and teaming up with Spektrum, they offer a lot of Bind & Fly, Bind & Drive, etc. models, meaning you get the model, with a Spektrum compatible receiver build in. Bind to your transmitter, and you are good to go.

Fly Sky, the protocol that is used by for instance a lot of Hobby King transmitters, is also used in some models, such as Ansmann and Team C. Also, compatible receivers are cheap, so it's easy to replace a non compatible receiver with it, to be able to use a single transmitter to control more models.



21: Can I use a stick transmitter to run a car, or does it have to be a pistol grip type?

Short, yes you can, and though for many a steering wheel feels more natural than stick, when driving an RC car, it can be done differently. What you need is a transmitter with at least 2 channels, and the sticks must be self centering. Some transmitters offer the option to change a stick between self centering and ratchet, so it can also be used for a plane for instance. On a car, you definitely want self centering.

One possible drawback of using a 2 channel stick transmitter on a car, is that is usually lacks a dual rate adjustment. On a pistol grip, this is usually present, and allows to set the steering throw electronically, to limit it such that the wheels don't bind when giving full steering input. Or maybe set this limit even lower, to make the car less twitchy. When you have a stick transmitter without the option to set this, and you do get the steering to bind when moving the steering stick to full deflection either side, the only option is to limit steering throw mechanically. So moving the steering rod between the servo and steering system closer to the center of the servo axle, so the steering rod has less movement. This may require some fiddling to get it just right, and having a simple dial to adjust it on the fly, is a big plus of pistol grip transmitters.

With that tackled, and having the ESC setup to match the throttle range of the throttle stick, you should be good to go.



22: Can I use rechargable batteries in my transmitter?

Although transmitters can usually last several hours or longer on a set of fresh alkaline AA batteries, eventually these will need replacing, and this can be a costly affair if you run your car often. So rechargable AA batteries will be convenient and cost effective. Most radios can run on these as well, but there are a few things to observe. Regular NiMh batteries often don't work, and have high self discharge. Even special batteries designed for use in digital cameras often fail, despite being quite expensive. What you need are low self discharge batteries, like Sanyo Eneloop, or the cheaper variant, Hobby King "LSD" (which stands for Low Self Discharge, and not the substance artists like the Beatles are said to have used for "inspiration") batteries.

Some transmitters still won't work on these batteries, then it's time to look at alternatives, like LiFe battery packs. With a voltage of 3.3v per cell, a 3S pack will be an excellent replacement for a 8 cell AA pack, and a 2S pack for transmitters that use 4 cell AA packs. In case you transmitter uses 6 AA batteries, a 2S LiPo will be the closest. If the transmitter lacks the option to set the low voltage warning, it's wise to use a seperate voltage monitor, to avoid deep discharge of the LiFe or LiPo pack.



23: My receiver antenna is broken, how can I fix this?

Depends on the type of transmitter/receiver. On "oldskool" FM or AM equipment, all that matters is the total length of the antenna wire, and the antenna is made from a single wire. So either replace with a new antenna wire, like by soldering directly to the board, taking a wire the same length as before the break occurred. Or add a new piece so the total length is the same again as before.

A 2.4 GHz receiver antenna is different, as it uses a coaxial wire. Only the center wire receives the signals, the coax shell acts as shield. So replacing the antenna by soldering a new one on the receiver boars, is more tricky. There is also another solution, the actual antenna is simply a part of the coaxial wire with the metal shield removed. So if there is still enough wire left, it can be enough to strip part of the metal shield, so you get again an exposed center wire part of the same length as before. It would help to have a good receiver of same type to measure how long the exposed part should be.



(continued in the next posting)
Last edited by SoloProFan; Oct 21, 2016 at 02:58 AM.
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Jul 21, 2013, 04:11 PM
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Part 2, covering Suspension, Drivetrain, Wheels and Tyres, Maintenance and Upgrades.




Suspension Setup



1) Do I really need oil filled dampers? Just plain springs will work fine too, right?

Indeed springs can help a car negociate bumps and so, but they are very limited. For best road contact you want the shock to move as lightly as possible, to react fast to bumps etc, but don't want the vehicle bouncing up and down several times after encountering an obstacle. With simple springs, that is what you get.

There is an option to use thick grease on the shock rods, called friction grease. These friction dampers already work better than just simple springs but the grease used tends to be very sticky to hands etc, almost like glue, and the damping action still leaves to be desired.

Oil filled shocks provide the best possible handling. The thickness of the oil affects the damping, as well as the shape of the piston, and the amount of holes and size of the holes in the piston. This way you can make the shock's response vary from silky smooth to much tougher. Quality shocks use o-rings to seal off the oil-reservoir, so these can't leak easily. To get an even better seal, you can use "Green Slime" or a similar product. But even if you have to fill up oil shocks on a regular basis, and sometimes remove all the old oil, and fill with new, the much improved road/terrain handling makes it all worth it.


2) Can I use any oil for shocks?

Although other oils might work, often these don't offer a stable damping response over a wide temperature range, and some oils may even damage the plastics and o-rings used. Silicone shock oil doesn't have this risk, and has stable viscosity over a wide temperature range. It comes in many thickness ratings, expressed in CST, CPS or WT. Problem is their relation is not linear. With the WT standard it can even be that one brand's 30 WT is not as thick as another brands 30 WT. CPS/CST doesn't have this problem, so it's easier to stick to that. To get an impression, soft, thin oils are up to 350, than till about 700 you have the medium thick oils, and till 1000 are the "hard" oils.


3) My car handles pretty badly, it bumps all over the place. Do I need to get new shocks?


If you already have oil filled shocks, and assuming you have tyres that provide good grip on the surface you run on, it could be the shocks just need some tweaking/cleaning. With the spring removed from a damper, does the piston move smoothly up and down? If you feel something binding, perhaps the piston rod is bent, or some dirt has found it's way into the damper and is now stuck between piston and shock body. If needed, remove the oil, and see how the piston moves then. It should move very freely, the resistance should come fully from the oil. As most pistons are molded plastic, it's possible burs are still present on the edges of the piston, increasing friction between the inside of the cylinder and the piston. Best way to check this is to remove the piston and rod from the shock, and insert the piston from above in the cylinder.

If that is ok, and the handling is still pretty bad, what thickness of oil are you using? RTR vehicles are often supplied with thicker oils, as this will prevent the car from bottoming out during the average abuse of a beginning driver, which often includes high jumps, as the driver is testing the car's limits. A hard setup will protect the bottom plate from scratches etc, but can also negatively affect the car's handling. Try a light oil and see how it goes with that, or if you have the choice between shock pistons with more or less holes, try those with more holes, allowing the oil to move more freely from one side of the piston to the other.

What can also help, if available, is mounting the shocks more to the outside on the suspension arms. This creates more "leverage" for the shocks, and they will respond to smaller bumps. This will also affect ride height or ground clearance, so keep an eye on that.


4) I'm going to get new oil shocks, but can't decide between the various types...


So, if you do need new shocks, either because the current ones are worn, broken, or your car currently has friction shocks or simple springs, you will find out there are different types. First there is the choice of metal vs plastic. Where with other car parts it's often a debate whether metal will be better than plastic, with shocks this debate is quickly settled. With plastic shocks there is always the risk of the shock caps popping off on a big impact, and the metal shock body tends to have less friction between it and the piston. Furthermore, some metal shocks have coated insides for even further reduced friction, like the "velvet" coating Kyosho uses, or Titanium Nitride coating, to name a few.


Then we have several types:

"Regular" shocks

For 1/10 scale this means a shock body diameter of around 12 mm, single shock body. Quite capable, for years this was the best possible option. RTR cars that come with oil shocks, are often fitted with these.


"Big Bore" shocks


As the name suggests, the shock body is bigger in diameter than regular shocks. The idea is that this improves damping, and it usually does. Beware though, sometimes the label "Big Bore" is just used for marketing, and one company's Big Bore shocks are the same as another brand's regular shocks...


"Piggyback" shocks

These shocks have a second oil reservoir, "piggybacked" on the main cylinder. Apart from looking a bit weird at first sight, it's supposed to have an advantage over regular and big bore shocks. The idea is that, even though silicone oil has quite constant thickness over a wide temperature range, the oil in the shock can get warmer during heavy action (remember all the impacts on the shocks are dampened with friction, in this case friction in a fluid, and where friction occurs, there is thermal energy aka heat) and will get thinner as a result. As with Piggy Back shocks you have more oil in the shock, it takes longer for it to heat up. But the advantage over regular big bore shocks, and even normal diameter shocks, is limited. Besides, if alu shocks are used the free air flowing over the shocks during running, will also help to prevent a signifcant temperature increase.

Apart from the limited advantage, if any, these are harder to (re)fill properly, and take up more space, sometimes limiting mounting options. So probably best left alone, unless you like the looks better than other shock types, and don't care much about the disadvantages.


5) My car pulls wheelies all the time, or does a 180 turn unexpectedly. It's very twitchy on the throttle...


Well, it could be you just need some more practice, just like with a real car. Especially a 2WD vehicle, with most weight to the rear, and combined with a powerful brushless motor and lipo battery, can be very twitchy. If possible, you could try to lower the ESC's start power, often called "punch" to soften throttle up. If your transmitter has expo-settings, you could also make the throttle response curve more gentle.

Apart from these electronic solutions, it won't hurt to look at the drive train. Is the slipper clutch adjusted properly? (See Part 2 "Drivetrain" for tips how to adjust the slipper clutch properly) If the rear shocks are too rigid, either from having thick oil, tough springs, or high spring tension setting, or a combination of these 3 causes, the rear is also more prone to act as pivot point. Lessen the pre-load tension on the springs, use softer springs, or thinner oil, so that the rear will be allowed to kick down a little upon acceleration, this absorbing part of the "blow" when you hit the throttle.

If that won't bring enough improvement, you could shift weight forward by moving the battery if possible, or add extra weight up front. Or get a wheelie bar, or fit a less powerful motor, as a car prone to making wheelies is often somewhat overpowered.


Some extra info:


Besides these basic tips, there is much more to setting up the suspension. It affects cornering, braking, jumping characteristics, etc. There are some excellent guides on the internet aobut this area, surpassing my expertise on the matter by far, so I'll post a few links here when I found these again.

Update: these links gives a nice overview of setup options for suspension and linkages:

http://users.telenet.be/elvo/ (click on "Quick Reference Guide" for a list of options and their effects)



Drivetrain

No matter how powerful your motor is, how much amps your battery can deliver, etc, it all doesn't mean much if you can't get that power to translate into forward motion. Tyres play a big role, as well as the earlier covered suspension, but the drivetrain is also very important. Here are a few things to observe.


6) What's the purpose of a differential (or diff), and how does it affect my car?

When a car makes a turn, the outside wheel has to cover more distance, as it runs over a bigger radius, than the inside wheel. This means the outside wheel has to spin faster than the inside wheel. With a rigid axle, that would not be possible, and this would stress the axle, wheels or tyres, especially on a high traction surface. The solution is a differential, it allows 2 axles to be connected and driven, but still be able to rotate at different speeds. As a result, no driven wheels are stressed, as each wheel can rotate at the speed needed to make the turn. This rather old video does an excellent explanation of the effect:
Around The Corner (1937) How Differential Steering Works (9 min 31 sec)


Besides helping in turns on high traction surfaces, the diff can also have some drawbacks. If on a 2WD vehicle one wheel loses all contact with the ground, the diff can allow it to "freewheel" and as a result the car will lose all traction and stop. This is something to be avoided. To do this there are 2 options, depending on the type of diff (short for differential) that is used.

Let's first cover gear diffs, that use an array of bevel gears (altthough other gear setups are also possible, but this type is most common in RC vehicles) to get the diff-effect. If you want to limit the "freeness" between both sides, thick grease, or filling the diff with very high thickness silicone oil (if the diff is sealed with o-rings against leaking) will limit the amount of independance between each outgoing axle. This will make the diff behave more like a rigid axle, but in lower grip conditions, that often offers better traction.

Another popular diff type in RC is the ball diff, that uses small balls clamped between two plates, to allow different rotation speeds between inner and outer wheel. Although these also use grease, this is not to finetune the amount of diff-action, but just for lubrication. The pressure between plates and the small balls can be adjusted to allow for more or less "freeness". This is less messy than using oil to fill a diff, and there is no need to take the diff apart to replace the oil, when adjustment is needed. But it may take some practice to fine tune this type of diff to best performance. Whereas with the gear diffs, if you know what thickness of oil is recommended for a certain car, you already have a good reference as starting point.

Finally, in very low grip conditions some cars offer the option to temporarily lock the diff, so it behaves like a rigid axle. When the car is back on high traction surfaces, the diff is better unlocked, for better handling under those conditions.


7) What is meant with "shimming the diff" and what is the benefit?


Shims are thin rings, sometimes as thin as 0.1mm, that are used to reduce play. These are used on wheel axles mostly, but can be applied on more places. If a car uses gear diffs, it's likely these will be made up with bevel gears. When under high stress, if there is play on the axles that the gears are on, this could make the gears move a little, and have worse gear mesh. This can damage the gears, and cause the diff to fail. As a precaution, you could take the diff apart, and use the right size shims to reduce this unwanted play. Don't overdo it, the gears should still be able to turn quite freely, but a little extre resistance compared to an unshimmed diff is ok as well. After some use, the diff will smoothen up a little anyway, as the gears start to wear in to each other.

It may take some time to get it right, but it will certainly enhance the diff's life expectancy. Some companies, like 3-racing, have conveniently packaged multiple thickness shims in one package, in that case 0.1, 0.2 and 0.3 mm, giving you more options. If a 0.3 mm is too tight, and a 0.1 too loose, you can use a 0.2 instead, and keep the 0.1s for moments where only a very thin shim is needed,


What's the purpose of a slipper clutch, and how do I set it properly?

A slipper clutch, or short, slipper, is used to make the coupling between spur gear and rest of the transmission less direct. As the name suggests, it allows some slip. This will shield the transmission from sudden high torque, like when accelerating full throttle. Most common way to achieve this is by having the spur gear "sandwiched" between 2 plates, with a thin layer of special somewhat rubbery looking material (these discs are called slipper pads) between the plates and spur surface. A spring loaded nut supplies the pressure and allows adjustment.

Like the ball diff, this slipper clutch takes some attention to adjust properly. Set it too tight and it will not help with sudden impacts on the drivetrain, increasing the risk on stripped gears, etc. Set it too loose, and the car will not be able to pick up speed fast, and accelerating will feel like driving on ice. The excessive slipping of the clutch can also cause the slipper pads to heat up and get burnt, rendering these unusable.

A common way to adjust the slipper clutch, is to first tigthen it fully, then start loosening it up. A general rule here is that, when giving full throttle from standstill, it should only slip the first few metres. You can often hear the slipper being active, as a sort of "squeal" coming from the transmission.

There are other methods, and as with most adjustments, after a while you tend to develop a feel for it, and you get to a good setting faster.



Wheels and Tires


Do RC wheels need balancing, just like on real cars?

With the lighter weights involved in an RC car compared to a 1:1 scale, this is often overlooked, or discarded as making only a marginally small difference. But in fact it can have much more effect on a car's handling and wear. Just pick up your car, and add throttle. Most likely you will feel vibrations, and probably can even see the ends of the suspension arms oscillate more or less with various throttle settings. This is mostly due to inbalance in the wheels. Remove the wheels, and perform the same test, and you should feel absolutely no vibrations, except from the gears.

Though with the wheels touching the ground they will have less freedom of movement to vibrate, inbalance in the wheels will make the holes in the suspension arms wear out faster, as well as all other pivot points in the suspension, including the steering and the attached servo. It can also cause screws to vibrate loose, though loc-tite should prevent that, it's clear that it's better to address the source of the vibrations, instead of countering it's side effects.

There are special tire balancer tools, in which you can suspend the tire, and check it's balance. When an inbalance is found, you can try to remove material on the heavier side, or add mass on the opposing side. When adding weight, make sure these are secured properly to avoid these weights flying of during a run.

A cheaper method for checking balance, while still fairly accurate, is taking a caster block, with bearings and axle, and mount the wheel. Hold the caster block pinched between your fingers, with the tire facing upward, then give the wheel a spin with your free hand. A well balanced wheel will need very little strength to hold the caster block, but one with inbalance will feel like it wants to break loose, and you will need to increase your pinch hold to keep it steady. A slight inbalance will probably not show up here, but only as you hold the wheel in it's normal position, but it will probably add little benefit when trying to eliminate this final minute inbalance. Final check is, as we started out, mount the wheels on the car, preferably one at a time, test for vibrations, add another wheel, check again, etc. When done with care, the result will be a car that runs without noticable vibration for it's entire throttle range, running more quiet, with less wear and more stability.


What tyres do I need?

Unfortunately there is no straight answer to that. What tyre will perform best often depends on conditions on the track or area where you drive, and also weather conditions. Generally, if you run offroad, you are likely to need more thread on the tyres, whereas a flat surfaces requires a more smooth tyre with less thread.

Besides the thread type, the hardness of the rubber also greatly affects tyre performance. A softer rubber compound will offer more traction, but on a high grip surface that might be too much, and the car will be more likely to do a griproll, meaning the car has so much sideways grip, the car just rolls over in a fast turn. Another drawback is that a softer rubber compound tends to wear faster. No problem if you have a money-tree in the backyard, and if you race in competition, you simply can't avoid having multiple tyre sets, for different race conditions. But most of us will probably be looking for a more cost effective solution, so a tyre that will offer good performance and will last more than a few runs.

Finding that tyre is usually a matter of trial and error, asking what more experienced drivers use. Personally, for casual driving, bashing, I prefer block pattern tyres, which offer decent traction even when using harder rubber compounds. Or V-pattern rally tyres, like these:



The latter have softer rubber compound than the block pattern tyres I use, but because there is more contact patch with the ground, the tyres don't wear fast at all. I'm still running my first set, whereas spike tyres of similar rubber softness would have been slicks by now...


How do I remove worn tires and fit new ones?

Sooner or later, tires will wear down, and require replacement. The easy way is replacing the wheel and tire, and buy pre-glued tires. But this limits your choices, and can be pretty expensive.

Another option is using tires that fit so tight around the rim, that there is no direct need to glue these to the rims as well. Especially when you don't run competition, this could do nicely.

The third option, which should be the most durable, is to remove the worn tire, and glue on a new one. To dissolve the glue holding the tire to the rim, there are 3 main methods:


1: Soak in Acetone. This fluid tends to dissolve CA-based glues, which are commonly used to glue tires. Fill a cup large enough to accomodate a wheel and tire with it, and put the wheel in. Make sure you do this on a well ventilated area, as it's a volatile fluid. Using gloves is also advised.

Apart from the health precautions you need to observe, there is a chance the plastic of the rims also gets affected by the soaking process, which can result in color chances, or even deformation.


2: Baking. Using a hot air oven to make the glue become soft, and remove the tire of the rim. Be careful of getting burned, and also here is the risk of damage to the rims, as the warm plastic can also easily be deformed.


3: Boiling: Putting the wheels in boiling water can make the CA glue become brittle, and as a result the tire can be peeled off the rim. Beware of the tire insert soaking up the water, which will be released as you handle the tire, and is still close to boiling temperature. Also, there is a risk of deforming the plastic of the rims while these are still hot.


Once you have succesfully removed the tires of the rims, the next challenge is to glue the new ones on. RCG member Paul Onorato posted an excellent tutorial on how to glue tires. Even though it covers SCT tires, the principles hold for most other tire types as well. You can find this tutorial here: https://www.rcgroups.com/forums/show....php?t=2138417




Maintenance




What tools do I need to service my car?

This partially depends on the car, but one tool will prove handy for a wide variety of cars, the cross wrench:




It contains 4 different size wrenches, 7mm, 5.5 mm, mm and mm. These will fit the wheelnuts, shock nuts, and some other too. Some brands include one with their kits, or RTR packages, if you don't have one, get it asap!

From here on the brand of car plays a role as some brands use Philips head screws (with a "plus" on the head) while other brands will use hex exclusively. Common hex sizes used are 1.5 mm, 2.0 mm and 2.5 mm, but beware, as your car may also be using the imperial system. Some of these tools may seem compatible, but you risk stripping the screw heads, so make sure you have the right size drivers.

Also beware of low quality cheap drivers, that often have such soft tips, you risk wrecking the screw's head, and won't be able to remove the screw the normal way afterwards. A few dollar spent extra here, will pay off quickly, as you don't strip heads, and are spared for the frustration that comes with this.

A very convenient thing to have, besides drivers and wrenches, is a car stand. I will provide a stable base to put your car on, also keeping the wheels off the ground, so your car can't run off if the wheels accidentally spin. Some stands are very basic, others have a rotating platform on top. Some have a magnetic patch on the sides, that can be used to temporarily store screws, so these won't drop to the ground. Some may have holders where you can place the shocks, for easy refilling these.



Do I need to clean my car after every run?

Though the initial answer would be "yes", as maintenance after every run will most likely keep the car in top condition, it's possible to save on time invested in this, and still have good lifespan for the car's parts. The decision whether to clean things, and even take apart certain sections of the car, depends much on the conditions you ran the car in. If you drove on a paved road, which was mostly clean, perhaps you will find a thin layer of dust on the tyres, and maybe the body shell, but apart from that the car didn't suffer much. In that case, a quick dusting off will usually do.

However, any surface involving water, requires if possible, immediate action. Especially when running on the beach, as salt water and sand are a car's worst nightmare. It can corrode bearings, and the sand tends to find it's ways everywhere, (just like when you have been on the beach ;-) ) and especially the drive train doesn't respond well to some grains of sand jammed between the gears.

There is a little debate about how to treat the bearings, some say it's just a matter of wiping dry, and adding a drop of oil. Some prefer to use a cleaner spray, like WD40, motor cleaner, etc, so flush the bearings, and then re-oil these. The main drawback of this method might be that cleaner residue stays behind in the bearings, or you flush out the valuable thick grease, that was put inside the bearings to ensure longest possible lifespan, and replacing it with a thinner oil, that doesn't have the same protection capabilities of the stock grease.

But that aside, you should do something, if you just put the car away, don't be surprised if the next time you take it out, some or more bearings have seized up, or are creating a lot of drag and noise.


Suppose you avoided the car getting wet, but drove on a dusty surface, so there is a bigger chance some moving parts have gotting very dusty as well. You can take everything apart, or do a simple test which gives a good indication if the dust entered the drive train. Take the pinion off the motor, and move the car forward and backward manually. If you feel extra drag, or some "grittyness" when moving the car back and forth, there is a good chance some dust/sand is compromising the moving parts, so you have to find out where it comes from.

If the car seems to be running smoothly still, don't be tempted to use compressed air to clean it, as you risk blowing sand/dust into the transmission, so the car may actually be worse after cleaning. A soft cloth, and a toothbrush are much more safe. Perhaps not as convenient as with compressed air, but it saves bearings.


Basic Maintenance

Apart from cleaning, some areas of a car require periodical attention, just like a real car would. Be sure to check on a regular basis for loose screws, nuts and bolts. Check if the suspension is still moving smoothly, and for signs of shocks leaking. A tell tale here can be dust sticking just below the cap, indicating some oil flowed from there, and caused the dust to stick to the cylinder. If you suspect a serious leak, refill the shock, and test it. Sometimes the o-rings at the bottom can leak somewhat. Tighter rings will help, but will also cause extra friction, so the shock can't move as smoothly as it should. Applying a little shock sealant, like the oddly named "Green Slime" can give that extra leak prevention, without hampering the shock's performance.

Check if the wiring and plugs are still ok, no conducting wire parts exposed, where these can cause short circuit, and if the wiring is still secured well away from moving parts, like a drive shaft.

If you didn't check for it during cleaning, remove the pinion from the motor-axle, and move the car around manually, to feel if the transmission is still moving freely, with no uneccesary drag.



Caring for brushed motors

In case you are still running a brushed motor in your vehicle, it will need special care. Due to arcing between the brushes and the commutator (which we will call "comm" from now on), a dark layer will form there, reducing the contact between these parts, and as a result the motor will become less powerful, and heat up faster. If you have a motor with consists of a sealed can, fixing this can be hard. You could try some comm/motor cleaner, and/or try to wipe the commutator surfaces with a cottom swab, but this is not easy. If you bend open the locking tabs on the rear of the motor, you can get better access to the brushes and comm. Still, this can be tricky, and usually closed can motors are cheap, so you might wonder if it's worth the trouble.

If you have a motor with removable rear section, also called the "endbell", there are more options to keep it in top shape. You can remove the springs that hold the brushes, slide these out, and clean the brush and comm surfaces with rubbing alcohol, or comm cleaner. You could also remove the endbell, for even easier access to these parts. For best performance, the comm should be trued on a special lathe. If that is not handy at the moment, or you don't want to spend the money on it, you can use very fine grain waterproof sanding paper. If you pinch the comm between thumb and indexfinger, with a piece of sanding paper wrapped around the comm. Then slowly rotate the axle while trying to apply even pressure, creating a "poor man's lathe" polishing the comm's surface. A real lathe will always be better, but when done carefully, this can work out pretty well.

After this polishing, clean the brushes and comm surface. With the comm, be sure to clean the gap between the copper colored sections, so no dust from sanding remains there. This can be done by carefully moving the tip of a knife through those gaps. Rebuild the motor, and let it break in again. If performed well, the motor will run much better than before, faster and cooler.



Upgrades


First, an upgrade that any car will benefit from, are ball bearings, if these are not already fitted. Some brands try to be economical and either fit plastic bearings (very bad) or self oiling bronze bearings (somewhat better) in their cars. These give higher resistance, and more wear than ball bearings and limit performance. Before considering any other upgrades, check if your car has ball bearings, and if not, fit these, for better speed, lower wear, and longer run time on your batteries.


Are metal parts better than plastic?

Often it is thought that replacing plastic parts with metal versions, is always better. Often the "bling" of the metal parts already makes a car look faster, more sturdy, etc. But despite the looks, it's wise to use metal parts with care. Plastic usually has some flex, this helps to absorb the impact of a crash. When a plastic parts is replaced with metal, the impact will get transferred to either another section of the car, or the metal part will bend. Also, metal parts, even when made from aluminium, are still typically heavier than their plastic counterparts. This means less performance of the car, and more energy to dissipate when the car hits something.

So, think well before replacing a plastic part with a metal one, if it will really improve the car, unless looks are more important than durability.


What's the purpose of CVDs aka Universal joints?

Getting the drive power to the wheels on a vehicle with independent suspension requires a flexing axle. A simple way to get this is a "dogbone" and drive cups.



Simple, and easy to take apart. Dogbones tend to be a little more noisy, especially as the suspension arms moving up, and the angle between drive cup and dogbone increases. Apart from that, sometimes dogbones can "pop out" under extreme stress, and the u-shaped openings in the drive cups wear out sooner or later.

CVDs or universal joints have an advantage, one of the drive cup/dogbone connections is replaced with a direct coupling, like this:



This type of drive axle will cause less resistance under an angle, which is mostly convenient on the front of a 4WD vehicle, where the wheels make multiple angles with the drive axle, as these need to steer, while the suspension arms move up and down as well. But these can also be used as upgrade parts for the rear wheels, making the drive train a little more efficient.
Last edited by SoloProFan; Feb 24, 2015 at 02:05 AM.
Jul 21, 2013, 04:12 PM
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Part 3, What to check when getting a Used RC Car.


I think most of us would prefer to buy new, unused, as you can then expect no problems, no damaged parts, etc. But when the budget doesn't allow a new car, or if the car isn't available new because it's since long time discontinued, like with vintage stuff, buying used is the only option. And you can still get a very good car this way, if you observe a couple of things:

1)If possible, to check out the car in person. Though we should assume that seller isn't trying to con us, there are sadly enough sellers that have no problems selling bad condition stuff for prices that are far over the top. Having the option to personally inspect the car to be purchased is one of the best ways to prevent making a bad purchase. If the seller is close enough to come on over, do ask to make an appointment. If a seller is offering bad goods, he will usually go to great lengths to avoid you coming over. Though there may be a good reason why you can't come over to check out the car, it's usually a sign of trouble when a seller tries to keep you away.

2) If you do get to see the car first, there are some things that can quickly give an impression of the condition of the car to be purchased.

- Check joints and links for slop. Some slop might be just a matter some things requiring tightening, or... it may be necessary to replace quite a few parts to get the car back in shape again. And then a bargain can quicky turn into a money pit

- Check the shocks for leaking. It's normal to have a very thin film of oil on the shock piston rods, but when you see drops or a very oily suspension arm, it's likely the shocks are leaking, and require a rebuild. This could involve getting new o-rings etc, so you need to take that into account when judging if the car to be purchased is a good deal, or not.

- See if you can feel how smooth the car runs. When pushing the car forward by hand, are there any "heavy" going spots, like something's binding.




(also reserved for adding additional FAQ related information)
Last edited by SoloProFan; Feb 23, 2015 at 10:15 AM.
Jul 23, 2013, 07:55 AM
Registered User
nice start on the FAQ thread this will answer many questions,
Aug 02, 2013, 06:17 AM
Paul Onorato's Avatar
Great idea SoloProFan.
Aug 02, 2013, 08:56 AM
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Quote:
Originally Posted by RcDragons
nice start on the FAQ thread this will answer many questions,
I certainly hope so. And should you feel like something is missing, just ask


Quote:
Originally Posted by Paul Onorato
Great idea SoloProFan.
Thanks, I'm trying to make it as comprehensive as I can, while trying to keep it practical.
Latest blog entry: For the love of the hobby!
Aug 02, 2013, 01:25 PM
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And I will try and contribute too. This will be a great resource.
Aug 02, 2013, 01:41 PM
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Contributions are very welcome, there are plenty areas in which my expertise is mostly theory. I do have some wide RC experience, as I also sail boats, fly small helis and even a small plane, but that's not enough, I feel.
Latest blog entry: For the love of the hobby!
Sep 03, 2013, 03:17 PM
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If something is missing from this attempt to make a FAQ, please chime in.
Latest blog entry: For the love of the hobby!
Sep 03, 2013, 09:08 PM
Sl33py sl33p
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Only question for me is on the gear mesh pic. Do you know what size pinion that is? great write up
Sep 04, 2013, 12:06 AM
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Quote:
Originally Posted by Sl33p3r
Only question for me is on the gear mesh pic. Do you know what size pinion that is? great write up
I would say, just count the teeth, pinions are described with their teeth number and teeth spacing ratio to diameter, called the gear's module. Size is irrelevant, as 2 pinions can have the same size, but different module, and be totally different in shape and appearance.

Glad you finf this useful, anything you would like to see added?
Last edited by SoloProFan; Sep 04, 2013 at 12:12 AM.
Sep 04, 2013, 12:16 AM
Sl33py sl33p
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no sir you nailed it
Sep 07, 2013, 11:44 PM
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91Atrac's Avatar
Great FAQ! Answered. Could questions I would have made a thread to ask the community hahha!

Question tho. What about piggyback shock vs spring an oil filled shocks..... I have some and would like to install those as I wanna be aggressive with my revo so the extra oil will help absorb large jumps

Right?
Sep 08, 2013, 01:48 AM
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Quote:
Originally Posted by 91Atrac
Great FAQ! Answered. Could questions I would have made a thread to ask the community hahha!

Question tho. What about piggyback shock vs spring an oil filled shocks..... I have some and would like to install those as I wanna be aggressive with my revo so the extra oil will help absorb large jumps

Right?
Thanks, and as for the shocks, good suggestion to dig a little deeper into the various shock types and how these affect handling. I might also cover different materials used, alu vs plastic, etc
Latest blog entry: For the love of the hobby!
Sep 08, 2013, 01:35 PM
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91Atrac's Avatar
Yea that and also different shock rods like titanium and coated ones too.


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